Starting from before the bronze age, laminating using a matrix or resin with a structural reinforcing fiber has contributed to strength in parts or surfaces. A good example of an old application includes the use of horse hair as a structural fiber with plaster serving as the matrix. After the development of resins like Bakelight, Bakeland (U.S. Pat. No. 1,216,265 February 1917) discovered after the turn of the last century, and glass fibers, first brought into use around WW II Slayter et al, (U.S. Pat. No. 2,692,219 October 1954), composite plastic laminates have shown up everywhere. Ranging from boats to car bodies to sports equipment to aerospace/satellites, there is a growing list of combinations that is too hard to keep track of and too numerous to mention. Representative examples include the more common combination of E-type fiberglass with polyester resin; a more elongation-homogeneous vinylester S-glass combination, a carbon fiber epoxy combination; a carbon fiber concrete combination and so on. Emerging types of laminates include systems where the resin can be a similar type of material as the fiber, i.e. “carbon/carbon” laminate. Here, after a fired set, the fibers can “aim” the strength in the preferred orientation while a carbon matrix would provide for unified thermal expansion characteristics (between the fiber and matrix) not to mention potentially very high operating temperatures.
Processes for laminating composites have branched out with even more divergence. “Spray and lay” might serve as the backbone of processes. A composition of E-glass “blanket” of matt may be wet out with polyester resin using a brush or spray gun, or both resin and glass could be distributed with a “chopper”, than rolled out till the laminate would be the resin/glass and void of dry spots and air bubbles. It would be particularly important to get out these dry places and air bubbles since they would cause weak spots in the laminate, not to mention allow for contaminates (i.e. moisture) to occasionally diffuse into the laminate.
Another method to get out the air (albeit with thinner less-detailed type laminates) includes the process of vacuum bagging. All the air is sucked out of the laminate giving the bag the same pressure as the atmosphere and forcing an outer blanket of material to soak up the extra resin as well as press the laminate against the tooling surface to give it as high of fiber/volume ratio as possible, while still causing the layers to be glued together.
Involving temperature in the process can vastly increase the wet-time and reduce the labor of vac-bagging. Using pre-impregnated fibers or “pre-pregs”, the fibers are already wet out, and already catalyzed. Either the increase of temperatures in an oven or allowance to attain room temperature from being previously chilled causes a temperature rise. The temperature rise allows prepregs to attain a set or cure while under the bag, while shipping, storage, preparation of material (i.e. loading the mold) occurs in a cold state before curing. More diverse types of resins such as thick viscous epoxy can be used when involving this process, however the process still is mostly limited to fairly thin layers of laminate per pass or per bagging.
Also considering heat, are the use of thermoresins where instead of chemically curing the matrix (i.e. thermoset resins: polyester, epoxy, vinylester etc.) the heat-meltable plastic (i.e. nylon, PET, PEEK) is melted. The bond is made between the hot plastic; when the laminate cools, it becomes hard and the part is done.
Other impregnation methods include types of Resin Transfer Molding RTM. (also Resin Injection Molding; RIM) In this process, high diffusion reinforcement is laid into a closed (i.e. male/female) mold and the resin diffuses throughout the surface of the part creating a “good-both-sides” laminate. Both Carter et al (U.S. Pat. No. 7,192,634 March, 2007) as well as Dunn (U.S. patent Ser. No. 0070183; publication date Mar. 31, 2005), have implications towards RTM type processes with channeling and re-melting or chemical wetting of fibers respectively. The challenge with RTM processes is that the resin must diffuse very easily and most likely it would need to be thin. The problem with this is when the resin chemically cures there is a likelihood that it shrinks and the ratio of fiber to volume would be less than with thick-pass layers, and there could be increased brittleness. Shrinkage even has consequences on surface quality: a large amount of shrinkage will cause “print-through” where the pattern of the shallowest layer shows up on the surface of the part. While thinner resins will wet out easier, there is most often a tradeoff between how much wetting can be done per layer vs. how much shrink can occur. A real low-viscosity resin will wet out more layers or thickness, but will tend to shrink more. A thicker resin will not do as well as a penetrating wet out but will shrink less. Less shrinkage not only has dimensional effects, but relates significantly to warping, surface caving, inner layer stresses (especially if previous layers are allowed to dry/set/cure. Because of this, many layers must be added separately to the laminate with the resin essentially gluing each layer to the previous one.
Functioning with both thermoset and thermoplastic resins and sometimes employing temperature differential is the process of pultrusion, and is to be found in Goldsworthy (U.S. Pat. No. 4,469,541 Sep. 4, 1984). Here is an example of where not only there is a pultrusion that can change its die-shape, but its die-cross-sectional surface area. There is also mention in Goldsworthy (1984) of pultruting inserted objects. The nature of pultrusion often implies much fiber that is unidirectional, long (with respect to the die shape) and therefore held together by glue strength. It should be noted that pultrusions can also be braided, or have braded skins. Beam loading forces on a pultrusion could enact sheer forces between compressive and tensile orientations within the laminate. And, as in a point load in the center of a beam supported at each end, there is a case where large amounts of sheering could take place at the supported ends and cause failure by splitting with unidirectional fibers and glue strength, or sheering between the top wall and bottom wall in a braided “tube” like structure. If there were lots of perpendicular fibers situated especially at the ends that could lock the unidirectional fiber or walls of a tube together, there would be much more strength and resistance against sheer, especially when more room for perpendicular laminating can be provided by lesser requirement for lengthwise orientation of fibers near the ends. This extra open space (the closer to the end, the more space) could be filled by substantially perpendicular fibers that would tie the ends together as exemplified in [FIGS. 15 and 16] regardless of how thick the pultrusion/beam would be and regardless if it contained an object or inclusion.
The problem with all these processes is that extra layers of laminate or passes have to be made. They have to be thin enough to get the air out, and because of this thinness, the layers have to be essentially glued together with the resin. Often in these multiple passes, the layers can easily delaminate
Limit for a Single Pass
Most of the time the fibers are treated with sizing that allows the resin to circulate and diffuse throughout the fiber blanket to help get it wet. If the fiber fails to locally get wet out or to a lesser effect, has air bubbles, the whole structure is weakened, not to mention coming up short of other properties like water tightness or aesthetic appeal. To be able to get out the air and homogenize the structure, there is a minimum amount of a layer that can be applied at once. If the layer is too thick, or if the inverse of the layer thickness vs. the viscosity of the resin is too far off, the resin will not wet out and circulate to the drier layers beneath. With this problem, the part could cure before the lamination can be properly rolled or brushed/blotted out. If running vac bags, the dry spot might not ever be compressed in the first place and the void will have strength not much greater than the pre-production fibers. Instead of a stiff strong lightweight part, the local dryness will have the same properties of fibers that are not wet out.
All of the former processes may imply representations of what one pass is. Examples are shown with the following list:
cloth (i.e. 4 oz/sq yd; 5 k tow 0 deg.; 90 deg.),
roving (6 oz./sq ft; 50 k tow 0 deg.; 90 deg.)
50 to 300 g/m^2, as found in (U.S. Pat. No. 6,599,610 Homma, et al, Jul. 29, 2003)
matt (0.75 or 1.5 or 3 oz/sq ft), E-Glass
10 mil surface or C-veil
1 to 50 g/m^2 as found in Mitani, et al, (Ser. No. 10/742,898 filing date Dec. 23, 2003)
Fabmat (roving sized in and stuck to matt), 5 oz/ft^2
5 k tow carbon fiber side-by-side 10 mil tape,
20 mil S-glass unidirectional tape
20 mil aramid unidirectional tape
The two common characteristics of this list are that 1. they are set up to be wet out in one pass; 2. they represent the relative thin skins that are involved in laminating. If there is a use for thicker skins, than additional passes need to be made.
Along with being weaved, the stitching of yarns and tows, fibers is commonly known in the art. These processes are always done in concert with sizing to make sure that the material is easy to wet out. Normally, a thin layer of resin sprayed over the blanket will adequately soak the resin after a minute or two. A 10 mil tape of carbon fiber will be thin because the intended resin to use with it, epoxy is very viscous, thick and difficult to handle. Fabmat that may have 1.5 oz/ft^2 sized and tacked onto, say, a 5 oz/ft^2 roving, will be intended to handle reasonably thin polyester resin. When the inventor laminated a typical epoxy with a 3 oz/ft^2 matt, the resin barely coated the surface. If it were not soaked in an overabundance of epoxy and laminated for an unexpectedly long time would have cured that way.
Carbon 5 k tows in the example list may be sewn together with a very thin strand group of glass so that they can be laid in as a unidirectional tape. Differing directions of fiber may be sewn together to provide strength in multi directions (i.e. 0 deg. sewn to 45 deg to 90 deg.). An example is found in Homma, et al (U.S. Pat. No. 6,599,610 Jul. 29, 2003).
In all of these cases,
1. The stitching is used to hold the component layers together throughout the process of lay-up.
2. The stitching is done while the reinforcement fibers are dry and before any wetting out and adding of curing agent.
2. The stitching is thin enough/wettable enough that it is easily wet out in one pass, but does not contribute significantly towards strength in the Z-direction.
Note that one pass refers to being able to wet out a blanket of reinforcement from the “top” and be able to reasonably have it get wet on the “bottom”. If there would be any fibers strong enough to have influences in the Z-direction, i.e. if the “Z” fibers would substantially add strength in the “Z” direction over the glue strength of the resin, they might not be able to be wet out in one pass. If a relatively thick tow were wet it could embroider two or more heavy wet layers against one another that would otherwise be too thick to wet out altogether. If layers were able to be tacked in advance with the tacking allowed to dry as in Youngkeit, (U.S. Pat. No. 4,938,824 Jul. 3, 1990) there could be a large risk of air or voids around the places where previous resin had dried and where it would have to be against newly-curing wet resin. Also in the process of filament winding/tape winding the process which is well represented by Youngkeit (1990) there is referencing to where the fibers slide, get smashed out or “peel or slough away” and for some irregular shapes waste material in “false domes”. If the tapes were to be tied around loops or hooks at the ends that could suspend the tension to some degree (as in [FIGS. 26, 27,28,29]) before the tape changed direction again, a degree of tension could be still maintained in the wrapping and peeling away could be minimized
In all the cases, the sheet or blanket of reinforcing fiber whether it is stitched-together components or not, is prepared to be wet or laid in a single pass; if the fabricator would lay down too many layers at once, or try to lay too much down without being able to wet it out, the part would need to be repaired or scrapped. While there are products that encourage sticking together of a dry layer to a fresh wet layer, this is often a region where the layers could come apart or de-laminate. Delamination can even occur between layers that were previously prepared together. An example could be where fabmat was used in a part. While fabmat is matt adhered (i.e. with sizing) or stitched to roving, there could be a separation between that matt and roving even though they were laminated on the same pass together. Delamination can occur due to physical stress in short term as well as chemical stress in the long term (as examplefied by “blistering”/bubbles that grow inside the laminate of boat hulls over a period of years).
Composites made up of resin/fiber combination or matrix fiber/fiber combination (like in ceramic) often can delaminate due to the tensile strength of the reinforcing fiber being greater than that of the glue-strength of resin. Causes of delaminating can include mechanical forces in the direction normal to the laminated surfaces, mechanical forces relating to sheering, chemical, thermal burn-offs, thermal shrinkages, variation of properties from layer to layer that include differing shrinkage rates of the layers, or changing properties causing sheering between materials of the layers. Further causes include differences or changes in properties which may include brittleness, ductility, elasticity, etc.
An example of a light weight sandwich comprising of inner and outer layer and pinned together is to be found in Rorabaugh, et al (U.S. Pat. No. 5,869,165, Feb. 9, 1999) similar is Fusco (U.S. Pat. No. 5,589,015, Dec. 31, 1996) Boyce, et al (U.S. Pat. No. 5,186,776 Feb. 16, 1993; U.S. Pat. No. 4,808,461 Feb. 8, 1989), Freitas (U.S. Pat. No. 5,466,506 Nov. 14, 1995), Windecker (U.S. Pat. No. 4,196,251 Apr. 1, 1980) et al. This is very lightweight and cost effective, however, if it were to involve embroidery, the hold-together material would be resin impregnated fiber tow, and would offer the opportunity for using the same type of resin and fiber as the outer laminates, Even if the wetted tow were heterogeneous, it would be much lighter, and more cost effective to embroider than to use pinning or the like to hold outer layers of a sandwich or the like together.
Weiss (U.S. Pat. No. 2,762,739 September, 1956) employs glass fiber in holding together outer layers sandwiching a foam core between. However, there is no mention of pre-wetting out the fibers which would lead to rapid drop in performance as the fibers could easily get frayed given abrasion, vibration, etc. If a pre-cured embroidered type system were to be worn, even cut completely through in places, all the other tow groups would still pass through the sandwich, and individually lock the outer layers together, thus allowing the partially damaged panel perform adequately as opposed to the whole system becoming unraveled.
Loyd (U.S. Pat. No. 4,109,435 Aug. 29, 1978) resists peel forces by means of barbed quill to hold substrates together. This and other like methods to prevent de-lamination would deposit extra metal in the laminate producing a heavier part than embroidering, and not work as effectively.
Chase (U.S. Pat. No. 3,837,985 Sep. 24, 1974) uses pins inserted into and tape wrap laminate in an ablation heat shield for a re-entry vehicle. This reference represents use of heterogeneous method, however does not anticipate the concept of unibody but rather comes in with the devices that tie together the system as an afterthought. In this invention, embroidery causes a tied together laminate to be a substantial unibody with layers, allowing possibility for embroidery, and layers of laminate to all cure at substantially the same time.
While Haung, et al in U.S. Pat. No. 4,350,728 (Sep. 21, 1982) have references to the problem of sheer in being a main problem of de-lamination of composite laminates as well as having mentioned peel issues, the current availability of high performance fibers joined with the technique as mentioned in this invention would trump the need for metal wire reinforcements to arrest de-lamination and prevent it from starting. In other words, pliable fibers such as aramid, running perpendicular to a wing spar would hold upper and lower laminates in spite of the event of a shear failure even though they may be loosened up. They would be lighter than metal, and if embroidered, would be less expensive to install, so would be doubly cost effective.
A torque box example is to be found in Hamilton et al (U.S. Pat. No. 6,277,463 Aug. 21, 2001) similar to a “box beam” rigid-structuring. This reference deals with de-lamination like filament winding which depends on “hoop” strength to do slightly better than the glue strength alone. A method of wrapping the perimeter of a laminate will not solve the problems that embroidering could, of a de-lamination of, say, a de-laminating T strut. Embroidering or needle pointing the core of a T strut would make it much much stronger over a folded perimeter wrap for that same part. Embroidering, as mentioned above in a wing spar could be employed as a safety measure that would prevent catastrophic failure in peeling and sheer, however if that same component were edge-wrapped, it would fail catastrophically once the glue strength started giving way. Other examples of where a wrap would fail would be in a case of thermal or chemical (i.e. corrosive) activities, especially when expansions or weakening of resin (as well as increasing the stresses) would occur.
Expansion issues specifically could include where a heated side of a laminate would begin to expand while a base layer would remain constant. Chemical activities could include where resin bubbles up form the inside and creates voids in the center of the layers, a phenomenon commonly known in the art.
All laminates like filament wound, wrapped, laid, with the exception of weaves within a single layer, and braids and the like would be at the mercy of this phenomenon.
Filament winding can provide lots of skin strength, and hoop strength, however, it is somewhat limited to geometric continuity. It would be impossible to filament-wind or wrap a bowl-shaped core. Tying can be done custom as may be wrapping or winding, but needle working-type processes can bring the laminate into concaves. It would be very difficult to wind complex shapes and the process does not lend itself to strengthening particular localities. Also, winding alone would not lend itself to having connecting spars that provide wall to wall strength, upper to lower surface strength, and the like, i.e. keeping the opposite walls from expanding apart from each other at poles. Embroidering type operations can be a good supplement to winding, in other words, wind, then tighten the concave parts down by embroidery, or tie off and bundle up a trunk at an end of a winding or wrap.
As mentioned earlier braiding in a pultruded part can be a way of strengthening the part and could be a very good way of preventing de-lamination of skin in a tube, or even in a tapered or formed object. This would be especially true in cases of where the skin of a tube can be braided. Embroidering again would be the only way to solve certain challenges that call for specific types of strengthening in specific ways. For example in a braided cylinder, there may need to be a lug that supports some kind of secondary part. Simply drilling a hole here would fray the braid, and surely weaken the pultruded braided cylinder. If the lug were to include an embroidery, and perhaps all layers could be ran wet, all the fibers of the braid would be still intact while the embroidery would provide the extra local strength it could be the way to add a “hard point”. Or if some of the tows of the braid were strained or broken, they could be made up for, and integrated back into the tube with embroidery. In this fashion, embroidery can be a good supplement to pultrusions. Another example of deficiencies in pultruding, wrapping or filament winding would be if there would need to be spherical tank laminated into a sheet or plate shaped composite structure: neither pultruding nor filament winding would very effectively do the job while embroidery would successfully take care of it.
Examples of third-dimension embroidering, sewing, etc are to be found with body armor examples. There is no mention made here of making a resin-fiber combination laminate in these, especially those formed in the pre-cured state. Such examples include Lundblad, et al (U.S. Pat. No. 5,456,974 Oct. 10, 1995), or with sacrificial-sheering embroidering elements as in Mazelsky (U.S. Pat. No. 5,512,348 Apr. 30, 1996). Embroidering done to a pre-cured system with pre-cured tow/strand would allow new possibilities for improving armor protection over the existing art, with the added protection from stabbing (i.e. armor-piercing stabs with a knife or spear) that rigid laminated armor would have over soft armor. When heterogeneous parts are mentioned in armor, it usually means pockets in a cloth garment or vest with hard parts or shields dropped in. In the armor art, there is little mentioned in the line of hard and soft together in an all-in-one unibody.
The possibility of laminating with heterogeneous materials at the same time are fairly common in the art, and an example of a heterogeneous composite laminate is to be found in Chase, et al (U.S. Pat. No. 5,350,614 Sep. 27, 1994). Although this reference also brings up stitching, it does not mention using tows in the pre-cured state, but instead favors RTM, resin transfer molding, which means dry prepping for the fibers as opposed to embroidering them in while wet.
Carter et al (U.S. Pat. No. 7,192,634 March, 2007) discloses a support structure of a curable composition that includes soluble or part soluble fibers that are stitched in with the reinforcement. While these soluble or part-soluble fibers can be considered as pre cured,
1. They represent the matrix, as opposed to the reinforcement in the final curable composition;
2. They anticipate that the layer is to be wetted out, laminated, bagged, RTM (etc.), in a single pass;
3. There would be no reinforcement fibers stitched in the final curable composition; as soon as the fibers are dissolved, they become the matrix and take on the same properties as the matrix;
4. The ultimately cured fibers, since being representative of the matrix and not reinforcing fiber will not improve strength in the “normal” or “Z” direction of an otherwise “X-Y”-local composition over the tensile strength or peel strength of the resin or matrix alone;5. And therefore soluble matrix stitching would not be able to improve upon the delaminating and or peel strength of the cured composition as the stitching of reinforcement fibers would.